A variety of ever-evolving wireless communication technologies have become necessities to daily living. The wireless communication technologies have evolved from 2nd Generation (2G) Code Division Multiple Access (CDMA) to 3rd Generation (3G) International Mobile Telecommunication-2000 (IMT-2000) in which data as well as voice is fast transmitted. Wireless Broadband (WiBro) or future-generation wireless communication systems are under development for faster data service than IMT-2000.
To co-exist with incumbent systems, the new wireless communication systems require different frequencies. However, since all available frequencies are occupied, a new frequency assignment within a few gigaherts is difficult and limited free frequency bands cause frequency interference between heterogeneous devices deploying a new wireless communication system. Yet, there are unused spectrums at or above 2 GHz and partially unused TV spectrums at or below 1 GHz. Hence, the Federal Communications Commission (FCC) has conducted a study on real spectrum use of these unused or under-utilized frequencies and sought comments on unlicensed access to unused frequencies through the Notice of Proposed Rule Making (NRPM) in order to increase frequency use efficiency.
In this context, J. Mitola introduced CR technology that senses an unused frequency or channel among allocated frequencies and efficiently shares the unused frequency. Although the CR technology is effective in solving the problem of limited frequencies, it is required that CR users do not cause harmful interference to authorized user, namely primary users by the frequency sharing.
Conventionally, a CR wireless communication system allocates explicit time-frequency resources as well as transmit power to Mobile Stations (MSs) by use of a scheduler, upon their service request. From the viewpoint of primary users that are charged for use of frequency bands, they may experience performance degradation due to inference from multiple users as well as a single user.
Accordingly, there exists a need for an apparatus and method for preventing multiple MSs from causing interference to primary users in a CR wireless communication system, when they transmit data simultaneously.